Soil gas sampling device and method



Aug. 6, 1940. G, L HASSLER 2,210,546

SOIL GAS SAMPLING DEVICE AND METHOD Original Filed Feb. 14, 1938 2 Sheets-Sheet 1 lnvenror: Gerald L. Hassler. 5g his AHOrncgL Q Aug. 6, 1940.

G; L. HASSLER SOIL GAS SAMPLING DEVICE AND METHOD Original Filed Feb.

14', 1938 2 Shets-Sheet 2 Jnvenior: Gerald L. Hassler. 5g his AH0rneg: TT

Patented Aug. 6, 1940 MET HOD

Gerald L. Hassler, Berkeley, Calif., assignor to Shell Development Company, San Francisco, Calif., a corporation of Delaware Application February 14, 1938, Serial No. 190,473 Renewed May 12, 1939 obtaining samples of gases seeping through the soil, and pertains more particularly to a gas sampler adapted to prevent any contamination of said soil gases by atmospheric air.

The present invention finds a particularly useful application in methods of underground exploration whereby indications of the presence of certain substances, such as oil, in or under a certain formation are derived from the analysis of gases drifting upwards to the surface of the ground by difi'usion through the surrounding formations. Thus, it is known that as an oil deposit is approached from any direction, the ratio of ethane or higher hydrocarbons to methane in said soil gases gradually increases owing to the fact that the higher hydrocarbons diffuse through the soil layers at a slower rate than methane. Since, however, the concentration of the hydrocarbons in the samples obtained from the soil is usually exceedingly small, amounting, for example, to about from 10 to 80 parts per million, it is obvious that any contamination of the soil gas samples by atmospheric air will lead to considerable errors and will make the inferences derived from the analysis of said samples entirely worthless.

It is therefore an object of the present invention to provide a method for sampling soil gases, wherein the latter are obtained from a confined sampling zone in contact with the ground, and a second, so-called guard ring zone, is interposed between the atmosphere and the sampling zone, the pressure in said guard ring zone being maintained at a value lower than that of the sampling zone to preclude contamination by atmospheric air seeping through permeable ground.

It is another object of this invention to provide a device of simple and rugged construction whereby soil gas samples may be quickly and efflciently obtained from any desired depth.

Other objects and features of this invention, as well as the construction of a preferred embodiment of the present sampler will be understood from the following description taken with reference to the attached drawings, wherein Fig. l is a cross-section view of one embodiment Fig. 2 is a diagrammatic cross-section of'another embodiment of the present invention.

Fig. 3 is a cross-section view of a form of the present device suitable for taking samples at,,the

native manometer arrangement for the present device.

The soil gas sampler may comprise a metallic rod 2, consisting of any desired number of sections connected together by means of couplings 5 such as shown at I 9, whereby the total length of the sampler may be made to vary from about 10 feet to 40 feet or more. A bit 30 is connected to the lower end of the sampler, and a head I to its upper end. The rod 2 is provided with; 10 passages or ducts 6, 9 and 22, running longitudinally therethrough. Instead of the solid rod 2 shown in the drawings, a hollow tubular rod may be equally well used, in which case the ducts 6, 9 and 22 are constructed in the 15 form of small diameter tubes made of copper or other suitable material.

The rod 2 is recessed to a smaller diameter at several places, as shown at 4, l2, l4 and 24. Infiatable packers 5 and I5 made of rubber tubing 20 or other suitable material are placed within recesses 4 and I4, respectively, and are securely aifixed to the rod 2 by means, for example, of wires or rings such as shown at l8, care being taken to insure a gas-tight fit.

The packers 5 and I5 are in communication on their inner side with the duct 9, connected at the surface with a tube 59 and pump 60, which may be of any desired mechanical or manual type.

An annular filter screen 8 is placed within 30 recess l2, which is located between packers 5 and I5 and is in communication with duct 6 and therethrough with tube 52 and a vacuum pump 63 placed at the surface.

An annular filter screen 28, which may be pro- 35 vided on its inner side with a silk lining 21 to prevent any silt or impurities from getting into the sampling system is placed within the recess 24, which is located below packer l5 and is in communication with duct 22 and therethrough 0 with a tube 56, gas sample reservoir 51, tube 55 and vacuum pump 63; provided with flow-regulating valves El and 62.

The packers 5 and I5, when in a deflated condition, and the screens 8 and 28 are placed within 45 the recesses 4, l4, l2 and 24, respectively, in such a manner that they are protected by the overhanging shoulders of the rod 2 from tear or abrasion by contact or friction with the ground when the rod 2 is driven through the ground.

In cases where it is desired to obtain soil-gas samples from a borehole which has been bored or drilled beforehand by means of an ordinary anger or drilling tool, a simplified device schematica-lly shown in Fig. 2 and operating in the 55 same manner as that of Fig. 1 may be used. This device comprises essentially two packers 5 and I5, which may be lowered and placed within the borehole by any desired means, for example, at the end of tubing strings 5, 9 and 22, made of any suitable material, such as rubber, copper, etc., and corresponding to the similarly numbered ducts of Fig. 1. To keep the packers properly spaced, they may, if desired, be interconnected by a rod III, of any desired cross-section. The rod 80 may or may not extend to the surface.

In cases where it is desired to obtain gas samples from the surface of the ground, without drilling a borehole, the device shown in Fig, 3 may be used. This device comprises tubes 6 and 22, connected to pump 53, as in Fig. 1. These tubes pass through and support an adapter II. A hood 12, made of a material such as rubber, impregnated silk, rubberized canvas, etc., and having any suitable shape, such as conical, semispherical, etc. is amxed to the adapter I l, a gastight fitting being secured between the tubes, the adapter and the hood. The hoodmay be provided with a suitable rigid frame or ribs (not shown in the drawings) to prevent it from collapsing when the space thereunder is evacuated. The tube 5 is terminated by an air filter 8 within the hood. The tube 22 is in communication, by means of an air filter 28, with the space within an open-bottom container 13, whose lower edges are adapted to be forced into the ground. The

container 13 and the hood 12 may be of any desired size: for example, the container l3 may have a diameter of 1 foot, and the hood 12 a diameter of 12 feet.

In operating the sampling device of Fig. l, the following procedure may be followed:

After a desired location for obtaining the sample had been selected, the lower section of the sampler, comprising the bit 30 and the screen 28 is driven into the ground, for example, by means of a sledge hammer, by clamp, block and tackle devices, or by applying pressure to the head I in any other desired manner. The next rod section is then screwed on top of the first, and the process is continued until the screen 28 has reached a desired depth, such, for example, as from 10 to 50 feet or deeper. The different sections forming the rod 2 are attached to each other in such order that the upper packer 5 is not less than about 5 feet from the surface of the ground, and preferably below the so-called hard pan, the distance between the packers 5 and I5 being usually about 1 foot. The distance between the lower packer l5 and the screen 28 is preferably about 10 feet.

After the rod 2 has been driven to a desired depth, the connections at the surface are made as shown in the drawing, and the packers 5 and I5 are inflated to any desired pressure within the strength of the material. A pressure of 10 lbs.

, per square inch will give a good seal between the Y packers and the fo ation, while a pressure of 15 lbs. per square in h will support a high vacuum below and atmospheric pressure above either.

of said packers, if the packers are of "gooch" rubber tubing. Although air is commonly used 53, the gases from space l3 being exhausted to the atmosphere, and the gases from space 23 being drawn through reservoir 51.

The space l3 between packers 5 and I5 is subjected to a higher vacuum than space 23 by properly adjusting valves 6| and 62, and forms a guard ring space around the sampling rod and hole. The purpose of this arrangement is not only to eliminate any possibility of leakage of the atmospheric air past the packers into space 22, wherefrom the gas sample is collected, but also to insure that said sample is not contaminated by any seepage or diffusion of the atmospheric air through a permeable formation along any such paths as shown at A. It will be seen that if the vacuum maintained in space I3 is of a higher order than the vacuum in space 23, no atmospheric air can penetrate within the space 23, since any fluid flow within the formation around and even immediately below the guard ring space will be toward said guard ring and not toward the sampling space. In this manner, the sample obtained from space 23 will be truly representative of the soil gases diffusing through the formation from below only, and the purity of this sample will be made independent of the permeability of the upper soil layers, and of the tightness of the packers.

In order to insure that the vacuum in space I! is higher than that in space 23, a manometer 58, such for example, as a U-shaped tube, filled with mercury or other suitable liquid is connected between tubes 52 and 55, the difference of the liquid level in the two branches, which may be suitably calibrated, indicating to the operator the existing vacuum diiierential which may be adjusted by means of valves GI and. 52. In general, this pressure differential should preferably be of the order of 1 centimeter of mercury.

In many cases, it is preferable to use five gaseous conduits or tubes instead of the three shown in Figs. 1 and 2. In such cases, as shown in Fig. 4, besides the tubes 9, 6 and 22, serving the same purposes as in Figs. 1 and 2, the present sampling device is provided with tubes 6A and 22A, opening respectively to the guard ring space l3 and the sampling space 23, the two arms of the manometer 58 being connected to said tubes 6A and 22A. In this manner, the readings of the manometer 58 are truly indicative of the pressure differences in spaces I 3 and 23, and are not influenced by effects arising from the viscous flow of gases in tubes 6 and 22.

In operating the device shown in. Fig. 3, the lower edges of the container 13 are forced into the ground to a depth of about 4 to 6 inches.

The outer edge of the hood I2 is then placed in contact with the ground and is covered with a sufficient amount of loose ground to prevent leakage, as shown at 14 and 15. The spaces within the hood I2 and the container 13 are then evacuated as before, a higher degree of vacuum being maintained under the hood 12 than under the container I3. The atmospheric air seeping through the permeable ground will then be directed towards the low-pressure space under the hood 12, as shown at A and A1, and only the gases seeping upwards from deep zones will find their way to the space under the container 13, as shown at B.

After operating pump 63 for a time sufficient to insure that all atmospheric air trapped within space 23 by inflating the packers had been removed from the system, the reservoir 51 is flushed with the soil air from the sampling space and is then filled with non-contaminated soil gases from space 23, whereafter the valves 50 and ii are closed and sealed, and the sample is ready for analysis. a I Itis understood that the present invention is v ,not limited to any of the particular embodiments described above, but relates broadly to a method and, apparatus for obtaining soil-gas samples, wherein the sampling zone is maintained at a pressure lower than that of the atmosphere, and a guard ring zone is" interposed between the sampling zone and the atmosphere, the pressurein said guard ring zone being lower'than that of the sampling zone. Thus, any desired amount of packers or seals may be used instead of two for the purpose of establishing the two essential zones described above, and these packers or seals may not necessarily be of the expansible or infiatable type. Any packer, even if it allows a cer- 0 tain amount of leakage between its periphery and the walls of the hole, is operatively satisfactory provided sumcient suction is properly applied to establish the pressure diflerential required according to they present invention between the sampling zone and the guard ring zone.

I claim as my invention: r

1. In a method for obtaining soil gas samples from the ground, confining a sampling zone in contact with the ground, maintaining said zone at a pressure below that of the atmosphere, confining and interposing a second zone between the sampling zone and the atmosphere, and maintaining the pressure in said zone at a value lower than that of the sampling zone.

2. In a method for obtaining soil gas samples from a borehole, confining a sampling zone in contact with the bottom portion of theborehole, maintaining said zone at a pressure below that of the atmosphere, confining a second zone in v contact with the walls of the borehole, said second zone being interposed between the sampling zone and the atmosphere, and maintaining said second zone at a pressure lower than that of the sampling zone.

3. In a device for obtaining soil gas samples, two spaced sealing means adapted to be placed above each other within a borehole in contact with the walls thereof, means for reducing the pressure in the space formed by the lower sealing means and the walls of the borehole to a value below that of the atmosphere, and means for reducing the pressure in thespace formed by the two sealing means and the walls of the borehole to a value below that of the space formed by the lower sealing means and the walls of the borehole. 4. In a device for obtaining soil gas samples,

two spaced expansible packers adapted to be placed above each other within a borehole, means to expand said packers into contact with the walls of the borehole, means for reducing the pressure in the space formed by the lower packer and the walls of the borehole to a value below that of the atmosphere, and means for reducing the pressure in the space formed by the two packers and the 5 walls of the borehole to a value below'that of thespace formed by the lower of the borehole.

5. In a. device for obtaining soil gassamples, two spaced expansible packers adapted to, be

packer and the walls placed above each other withina borehole} a first gaseous conduit passing through-thegtwo packers and opening to the outside belowqthe lower packer, a second gaseousafc'oriduit passing through the upper packer and opening to the out- (5 side between said two packers, means to expand and opening to the outside below the lower packsecond vacuum being higher than said first vacthe packers into contact with the walls of the borehole, means comprising said first gaseous conduit to reduce the pressure in the space formed by the lower packer and the walls of the formation to a value below that of the atmosphere, and 5 means comprising said second gaseous conduit to reduce the pressure in the'space formed by the two packers and the wallsof the borehole to a value below that of the space formed by the lower packer and the walls of the borehole.

6. In a device for obtaining soil gas samples, two spaced expansible packers adapted to be placed above each other within a borehole, a first gaseous conduit passing through'the two packers 15 er, a second gaseous conduit passing through the upper packer and opening to the outside between said two packers, means to expand the packers intocontact with the walls of the borehole, manometer means at the surface in gaseous communication with the space formed by the lower packer and the walls of the borehole and with the space formedby the two packers'and the walls of the borehole for indicating the pressures in said two'spaces, means comprising said first gaseous conduit to reduce the pressure in the space formed by the lower packer and the walls of the formation to a value below that of the atmosphere, andmeans comprising said second gaseous conduit to reduce the pressure in the space formed to a value below that of the space formed by the lower packer and the walls of the borehole.

7. In a device for obtaining soil gas samples, a rod adapted to be. placed in a borehole, said rod carrying at least two spaced packers adapted to form a seal with the walls of the borehole, means for maintaining a vacuum in the space confined by the lowermost packer and the walls of the hole, and'means for maintaining a vacuum in the space confined by the two packers and the walls of the borehole. said second vacuum being higher than said first vacuum.

8. In a device for obtaining soil gas samples, a rod adapted to be placed in a borehole, at least two spaced expansible packers carried by said rod, means to expand said packers into sealing contact with the walls of the hole, means for applying a vacuum to the space confined by the lower packer and the walls of the hole, and means for applying a vacuum to thespace confined by the two packers and the walls of the hole, said second vacuum being higher than said first vacuum. V

9. In a device for obtaining soil gas samples, a rod, a bit on the lower. end of the rod, means for driving said rod into the ground, at least two spaced expansible'packers carried by said rod, means to expand said packers into sealing contact with the formation surrounding said rod, means for applying a vacuum to the space confined by the lower packer and the formation, and means for applying a vacuum to the space confined by the two packers and the formation, said 5 uum.

10. In a device for obtaining soil gas samples, a rod, a bit on the lower end of the rod, means for driving the rod into the ground, at least two 70 spaced annular recesses on said rod, inflatable packers mounted on the rod within said recesses,

rod, means for applying a vacuum to the space confined by the lower packer and the formation, and means for applying a vacuum to the space confined by the two packers and the formation, said second vacuum being higher than said first vacuum. v n

11. A device for obtaining gas samples from the ground, said device comprising a first sealing means having its peripheral edge in gas-tight contact with the ground, whereby a gas-filled sampling space is defined by said sealing means and the ground, a second sealing means having its perpheral edge in gas-tight contact with the ground, said second sealing means being spaced from said first sealing means, whereby a second gas-filled space is defined by said two sealing 12; Ina method for obtaining soil gas samples from the ground, confining a gas-filled sampling zone in contact with the ground, maintaining saidzone at a pressure below that of the atmosphere, confining and interposing a second gas- 'fllled zone between the sampling zone and the atmosphere, maintaining said second zone at'a pressure below that of the atmosphere, and regulating the ratio of the pressures in said two zones. 15

GERALD I. HASSL'EB. 

